You are in: eMedicine Specialties > Radiology > VASCULAR/INTERVENTIONAL Angioplasty, Renal ArteryArticle Last Updated: Mar 30, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Coauthor(s): Alan Cousin, MD, Consulting Staff, Department of Radiology, Bayfront Medical Center Editors: Gary P Siskin, MD, Associate Professor, Department of Radiology, Albany Medical College; Chief, Division of Vascular and Interventional Radiology, Department of Radiology, Albany Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Douglas M Coldwell, MD, PhD, Professor of Interventional Radiology, Department of Radiology, Professor of Interventional Radiology, University of Texas Southwestern Medical Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Kyung J Cho, MD, FACR, William Martel Professor of Radiology, Fellowship Program Director, Department of Radiology, Division of Interventional Radiology, University of Michigan Medical School Author and Editor Disclosure Synonyms and related keywords: Renal artery, renal angioplasty, PTA, percutaneous transluminal angioplasty, percutaneous transluminal renal angioplasty, PTRA, renal artery stenting, renovascular hypertension, renal artery stenosis, RAS, renovascular hypertension, atherosclerotic renal artery stenosis, ARAS BACKGROUNDSection 2 of 11
  History of the procedure Percutaneous transluminal angioplasty (PTA) of the renal artery has become an increasingly widespread peripheral vascular intervention for the treatment of renovascular hypertension (HTN). Catheter-based procedures began in 1964 when Charles Dotter initially developed PTA for treating peripheral vascular atherosclerosis. Andreas Gruntzig revolutionized the technique in 1974 when he developed a soft, flexible, double-lumen balloon catheter for use in coronary arteries. PTA has since rapidly evolved into a widely used, versatile, and dependable vascular interventional technique. Excellent results can now be achieved in the renal arteries if patients are well selected and if experienced clinicians perform the procedure. Renovascular HTN and renal PTA In the United States, renovascular HTN is present in approximately 4% of the total population with HTN. It is associated with an increased morbidity rate because it adds the risk of renal insufficiency to the consequences of severe HTN. Traditional therapeutic modalities that include drug therapy and surgical revascularization have too many shortcomings. Medicines frequently fail to adequately control the patient's BP adequately despite polypharmacy, they can cause undesirable adverse effects, and patients may be noncompliant. Moreover, lowering the BP in presence of severe renal stenosis may lead to ischemic renal atrophy. Surgery imparts considerable morbidity, and results vary. The associated need for general anesthesia may cause complications in patients, who are often poor candidates because of diffuse atherosclerosis or renal insufficiency. Nonetheless, the correction of renal stenosis is considered the treatment of choice whenever feasible. Since its introduction in 1978, percutaneous transluminal renal angioplasty (PTRA) has emerged as a highly effective technique for the correction of renal artery stenoses. Renal angioplasty has notable physiologic, psychological, and economic advantages over other treatment modalities, and it should now be considered the therapy of choice for renovascular HTN. INDICATIONS FOR PTRASection 3 of 11
The indications of renal angioplasty are still evolving. The common indications are as follows:
PATHOPHYSIOLOGY OF RENAL ARTERY STENOSISSection 4 of 11
Renal artery stenosis (RAS) has multiple causes, but most lesions are due to atherosclerosis. FMD is the second most common etiology. Incidences of etiologies The Cooperative Study on Renovascular Hypertension included 2442 patients with HTN, 884 of whom had RAS. In 557 patients (63%), the etiology was atherosclerosis. In 286 patients (32%), RAS was due to FMD, and in 41 (5%), a miscellaneous etiology was identified. In the University of Virginia series, the etiologies were as follows: atherosclerosis (75 patients, 93 lesions), FMD (27 patients, 30 lesions), renal transplantation (7 patients), venous bypass (3 patients), and previous irradiation (1 patient). Incidence of RAS The incidence of RAS in patients undergoing cardiac catheterization is as follows: (1) RAS occurs in 62% of patients with peripheral vascular disease (PVD) and HTN.1 (2) RAS is found in 33% of patients with coronary artery disease (CAD). (3) About 18% of patients with CAD have stenoses of greater than 50%.2 (4) Both CAD and renal insufficiency are independent predictors for RAS. (5) The incidence of bilateral RAS is approximately 46%.3 Regarding asymptomatic RAS, as many as 50% of patients with RAS do not have HTN. The incidence of progression of RAS is variable, but progression occurs in most patients. The overall progression rate is 49%, with 14% of patients developing total occlusion. Serum creatinine values do not adequately mirror progressive anatomic disease, and control of HTN does not thwart progression of RAS. The absence of HTN after PTRA does not preclude restenosis. RAS is frequently underdiagnosed. Atherosclerotic RAS Atherosclerotic RAS (ARAS) is a common condition that is often but not necessarily associated with HTN. Because of its progressive nature, ARAS is becoming one of the leading causes of end-stage renal disease (ESRD). Indeed, ARAS is reported to progress within 5 years in 51% of patients, and renal atrophy develops in 21% of patients in whom ARAS is initially greater than 60% of the caliber of the vessel. According to the United States Renal Data System database, ARAS accounts for as many as 12-14% of all new patients entering a dialysis program each year. The overall annual cost for patients with ESRD is around $12 billion. The economic burden due to this disease and its consequences are huge, as are the potential savings achievable by preventing the progression of stenosis. The exact prevalence of ARAS in the general population is unknown because many cases of ARAS remain undetected. However, angiographic studies in patients with CAD indicate a 30% prevalence of ARAS. In one half of the cases, the narrowing is greater than 50%, and 4% of all cases involve bilateral lesions. In elderly patients, in those with atherosclerotic PVD, or in those with malignant HTN, the prevalence of ARAS may be higher, approaching 50%. This rate is likely to increase in the future as the population ages and as the frequency of diabetes mellitus increases. In a national survey in Italy, among 459 hypertensive patients referred to 19 HTN centers because of a clinically suspected renovascular HTN, 176 (38%) had angiographically proven ARAS. Moreover, in 76%, ARAS was greater than 70%; in 65 patients (37%), it was bilateral. Renovascular disease: clinical indicators Clinical indicators of renovascular disease are as follows:
These epidemiologic data emphasize the need for an aggressive diagnostic approach and treatment of ARAS for the treatment of HTN and for the prevention of ischemic nephropathy. Both those goals can be achieved, to some extent, with PTRA. PATIENT SELECTION FOR PTRASection 5 of 11
Renovascular disease is present in 10-40% of patients with ESRD, who constitutes the fastest-growing group of patients with ESRD. Nonselective correction of RAS has led to disappointing results. Most groups that compared conservative treatment with angioplasty found only modest or no beneficial effects of angioplasty on renal function and BP. Patients with a high likelihood of a favorable response should be identified. Factors that affect outcome include the severity of RAS; the procedure used to treat RAS (eg, antihypertensive drugs, angioplasty with or without stents, surgery); nephrotoxicity to radiologic contrast materials; atheroembolism; and most importantly, underlying renal disease forestalling a favorable response in renal function or BP, even after the successful correction of RAS. Renal resistance may be evaluated by using Doppler ultrasonography or captopril scintigraphy to determine if patients might or might not respond to intervention. Each factor must be considered before the correction of RAS to achieve satisfactory results in improving renal function and BP. Diagnostic studies for renovascular disease Diagnostic studies for renovascular disease include the following:
INDICATIONS, CONTRAINDICATIONS, AND SUCCESS RATES OF PTRASection 6 of 11
Indications for PTRA or renal stentingIndications for PTRA or renal stenting include the following:
Contraindications for PTRA or renal stentingContraindications for PTRA or renal stenting include the following:
Clinical success ratesSeveral published series report clinical results obtained with angioplasty. Fibromuscular dysplasia FMD When the cause of renal stenosis is FMD, the results of PTRA are uniformly good, with cure in about 58% of patients, improvement in 35%, and failure in 7%. These results are comparable to those obtained with surgery. Restenosis is uncommon in patients with this condition, and follow-up angiograms ( <5 y after angioplasty) often show no trace of stenosis. Atherosclerosis When atheroma causes the stenosis, the results of revascularization are not as good, with cure in 22% of patients, improvement in 57%, and failure in 21%, whichever modality (angioplasty or surgery) is used. Furthermore, in patients with diffuse atheromatous disease, the complication rate with both surgery and angioplasty is relatively high, and medical therapy may be preferred. The common indications for renal stenting include ostial stenosis, flow-limiting dissection of the renal artery after PTA, persistent significant gradient after PTA, and restenosis after balloon angioplasty. Short balloon-expandable stents are usually used for renal stenting. CLINICAL OUTCOMESSection 7 of 11
Early decrease in BP In patients in whom PTRA is technically successful, a prompt decrease in BP is usually observed. The mechanism of this early decrease is not understood. Plasma renin activity, norepinephrine, and muscle sympathetic nerve activity all increase in the first hour or two, despite the falling BP. This finding raises the possibility that some vasodilator substance is released. In the atheromatous patients with unilateral stenoses, the eventual benefit rate (defined as an improvement or cure of the HTN 3 months after angioplasty) was 87%, and in the FMD patients it was 92%. Patients with stenosis and a solitary kidney are excellent candidates, and one series showed a benefit rate of 92%. Table 1. Success Rates of PTRA in RAS due to Atherosclerosis (80% of RAS) and FMD (20% of RAS)
Adapted from Bajwa, 1998; Henry, 1999.10, 11 *Ostial location is an independent predictor of poor outcome. Clinical success rates are 54% at 3 years, with high restenosis rates. Effect of BP in ARAS Differences in the criteria used to select patients, in defining an improvement in BP, in the duration and modalities used for follow-up, and in medical treatment hamper any comparison of studies addressing the effects of PTRA on BP. Despite these limitations, authorities generally agree that reduced BP with PTRA in patients with ARAS is rare. In a review of the experience in 10 centers, 691 patients were treated with PTRA. About 19% were cured, 51% improved, and 30% had unchanged BP. In other reviews, the effects on BP were even less encouraging. For instance, 8% of several hundreds of patients with HTN were cured with PTRA. In a study by the present authors, 66 patients were followed up for at least 6 months, and the patency of the dilated artery was confirmed mostly by means of echographic Doppler velocimetry; in these patients, the rate of cure was 3%, with a 38% rate of improvement. Moreover, the introduction of stents has not improved the outcome of PTRA regarding BP. A 4-year follow-up study of 163 patients successfully treated with stent implantation showed that only 1 was cured, and 42% had improvement. These negative results are not surprising if one considers that the great majority of patients with ARAS have been exposed to the deleterious effects of high BP for years. Their HTN results in extensive renal and vascular damage, which prevents BP from returning to normal levels, even after the stenotic artery is dilated. This conclusion obviously stresses the need for the careful selection of the few patients who may benefit from dilation procedures. For patients who do not fulfill the diagnostic criteria for real renovascular HTN and for those in whom even PTRA is considered too risky, medical treatment permits the same degree of BP control achievable with dilation. Indeed the 3 major studies that compared the effects of PTRA and medical treatment in patients with ARAS showed that the BP reductions obtained with the 2 approaches were similar. The only advantage for patients treated with PTRA was diminution of their drug regimen. Table 2. Success Rates of PTRA in RAS due to Atherosclerosis (80% of RAS)
Adapted from Kidney, 1996; Dorros, 1993; Weibull, 1991.12, 13, 14 Effect on renal function Theoretically, PTRA should be used more for preserving renal function than for reducing BP. Given the progressive nature of ARAS, PTRA should be performed before the ischemic damage to kidney has occurred. Renal outcome with PTRA is better when renal function is still normal than when it is altered. In general, the overall cardiovascular risk for patients undergoing PTRA with a baseline serum creatinine level greater than 1.5 mg/dL is 5 times higher than that of patients with a creatinine level below that value. So far, no medications can retard the progression of ARAS. On the other hand, no evidence supports the theory that PTRA improves renal function in patients with ARAS. A large meta-analysis, 25-53% of patients undergoing PTRA had some improvement in renal function. In another review of 215 patients with ARAS and mild renal insufficiency treated with stent implantation, 35% had improvement in renal function, as estimated by assessing the changes in serum creatinine or creatinine clearance. In another 35% of these patients, the condition was stabilized with the procedure. Apparently, even for preserving renal function, PTRA should be performed only in patients who have been rigorously selected. Patients who might benefit from PTRA should be evaluated to the same extent as those chosen for a possible antihypertensive effect. Table 3. Effect of Renal Stenting on Serum Creatinine Level
Adapted from Henry, 1999.11 Markers of the outcome Unfortunately, no consensus exists regarding valid markers of a favorable renal outcome with PTRA. One may use the radioisotopic technique, which allows an accurate evaluation of the split function of the 2 kidneys. This method may eliminate the limitations inherent to assessments based on creatinine and creatinine clearance. The preservation of the renal function depends not only on the restoration of renal blood flow but also on the wearing off of other ischemia-induced mechanisms of renal damage that may fully regress only after a long period. PTRA can affect the glomerular filtration rate (GFR) of the dilated kidney and baseline values of peripheral plasma renin activity and angiotensin II (Ang II). These changes may suggest that the degree of activation of the renin system could be a predictor of the functional recovery of the kidney. From a mechanistic point of view, this finding fits well with the notion that Ang II is essential for the maintenance of GFR. Indeed, if renin is released in proportion to the reduction in renal blood flow, it is entirely plausible that the ischemic kidneys exposed to the highest concentration of Ang II are also those in which the GFR may increase when the renal blood flow is restored with successful PTRA. COMPLICATIONS OF PTRASection 8 of 11
The rate of restenosis in patients with atheromatous disease has been reported to be 19% after 9 months and 35% if the lesion is ostial. The latter rate may be an underestimate. In the randomized study by Weibull,14 the 1-year rate of restenosis was 25%. Losinno et al reported a 5-year patency rate of 82%, though this percentage was based on an incomplete sample of patients. Other complications of angioplasty include hematoma at the puncture site, azotemia due to the dye load, and cholesterol emboli. These complications tend to be more common in old patients with diffuse atheromatous disease than in others. When PTA is performed in patients with elevated creatinine levels, alternative contrast agents such as carbon dioxide and gadolinium-based contrast agents may be used to minimize the risk of azotemia as a complication of renal angioplasty. Findings from early clinical experience suggest that distal protection devices that are used during stenting of carotid arteries can effectively filter debris produced during renal angioplasty and stenting, preventing renal failure. However, gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffnesswithtroublemoving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Dissection or occlusion of the renal artery may also occur, but this is rare. When this complication occurs, renal stenting can restore renal blood flow. Acute pulmonary edema as a complication of angioplasty has been reported in a patient with bilateral RAS. In 1 large series, the 30-day mortality rate was 2.2%, and all deaths occurred in patients with atheroma. Table 4. Natural History: Progression of Medically Treated RAS
Adapted from Medical treatment arm of a longitudinal study of medically versus surgically treated patients with documented RAS followed up over 36 months.15 SUMMARY AND FUTURE TRENDSSection 9 of 11
Alone or in combination with stent implantation, PTRA is increasingly used as an alternative to surgical revascularization for the treatment of RAS, which may cause HTN or jeopardize renal function. The technical success is usually achieved in more than 85% of cases, with 10% failures. PTRA-related complications are observed in 7% of patients. An overall benefit on BP control is observed in 20-40% of patients with ARAS and in 60-70% of those with FMD. Independent of the etiology, PTRA appears to be technically effective in correcting RAS. However, the position of PTRA with respect to medical or surgical treatment needs to be better delineated through randomized, controlled studies aimed at comparing the clinical efficacies of these different approaches. MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Angioplasty, Renal Artery excerpt Article Last Updated: Mar 30, 2007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
